Droplet based microfluidics has become very popular, both in research and application.
To compartment extremely small liquid volumes into droplets and manipulate them offers
the benefit of inhibiting dispersion and cross contamination of analytes in chemical and biological application.
We present ongoing experimental research about the formation of droplets by the breakup of a liquid filament.
This non-equilibrium process arises from the interplay between flow properties and interfacial instabilities
that occur when the filament confinement is suddenly decreased. Despite a large number of studies on droplet
breakup, the physics behind this mechanism is only poorly understood. Here, we provide experimental evidence
that the breakup mechanism can be controlled by tuning the Capillary number and the channel geometry. In particular
we investigate the transition between two well-known breakup mechanisms: the step- and the jet-regime. Interestingly,
we observe the emergence of new breakup mechanisms within this transition regime.
Additionally, we also discuss the possibility to control the organization of particles dispersed within a droplet.
This passive concentration effect depends on the channel geometry as well as on droplet dynamics and particle properties
and does not rely on any external fields. It might be used to concentrate and wash particles that are frequently used as a
solid support or catalytic surface in biochemical reactions.